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이름만 다른(표기 변형) [[위키링크]]를 대상 문서의 canonical 제목으로 치환해 끊겼던 1,200개 링크를 연결. 제목/파일명 정규화 일치만 적용하고 별칭 매칭은 과병합 위험으로 제외(애매성 가드). 원본은 _link_reconcile_backup/ 에 백업. 도구: Datacollect/scripts/link_reconcile_apply.mjs Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
185 lines
5.2 KiB
Markdown
185 lines
5.2 KiB
Markdown
---
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id: wiki-2026-0508-load-balancing-strategies
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title: Load Balancing Strategies
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category: 10_Wiki/Topics
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status: verified
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canonical_id: self
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aliases: [Load Balancer, LB, Reverse Proxy]
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duplicate_of: none
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source_trust_level: A
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confidence_score: 0.9
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verification_status: applied
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tags: [networking, load-balancer, nginx, envoy, haproxy, aws-alb]
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raw_sources: []
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last_reinforced: 2026-05-10
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github_commit: pending
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tech_stack: { language: Config, framework: Nginx/Envoy/HAProxy/AWS }
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---
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# Load Balancing Strategies
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## 매 한 줄
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> **"매 LB = traffic 분산 + health check + sticky"**. 알고리즘은 균등성과 affinity의 trade-off.
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## 매 핵심
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### 매 알고리즘
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- **Round-robin**: 순차. 단순, 동질 서버.
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- **Weighted RR**: 용량 차등.
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- **Least connections**: 활성 연결 최소. long-lived 적합.
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- **Least response time**: 평균 응답 + connection 수.
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- **IP hash**: client IP→server. session affinity.
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- **Consistent hash**: cache/shard. node 추가 시 K/n key만 재배치.
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- **Random / P2C**: power of two choices, least-loaded 선택. 간단·강력.
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### 매 Layer
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- **L4 (TCP/UDP)**: 빠름, opaque. NLB, HAProxy TCP mode.
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- **L7 (HTTP)**: header/path 기반 라우팅, TLS 종료. ALB, Nginx, Envoy.
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### 매 Health check
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- Active: /health 주기적 GET
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- Passive: 실제 요청 실패 카운트
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- Slow start: 신규 노드에 점진적 traffic
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- Outlier detection (Envoy): 연속 5xx → eject
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### 매 Session affinity (sticky)
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- Cookie-based (LB가 cookie 발급)
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- Source IP (NAT 뒤에 모이면 unbalanced)
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- Header-based (custom)
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### 매 응용
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1. Web app: ALB + multi-AZ
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2. gRPC/HTTP2: Envoy (L7 multiplex)
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3. DB read replica: ProxySQL, PgBouncer
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4. Cache shard: consistent hash (Redis cluster)
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5. Service mesh: Envoy sidecar (Istio, Linkerd)
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## 💻 패턴
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### Nginx upstream
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```nginx
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upstream backend {
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least_conn; # algorithm
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server app1:8080 weight=3 max_fails=3 fail_timeout=30s;
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server app2:8080 weight=1;
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server app3:8080 backup; # only if others down
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keepalive 32;
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}
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server {
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location / {
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proxy_pass http://backend;
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proxy_set_header Host $host;
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proxy_next_upstream error timeout http_502 http_503;
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}
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}
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```
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### HAProxy
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```
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backend web
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balance leastconn
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option httpchk GET /health
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server s1 10.0.0.1:8080 check weight 100
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server s2 10.0.0.2:8080 check weight 50
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cookie SRV insert indirect nocache # sticky
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```
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### Envoy (L7, gRPC)
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```yaml
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clusters:
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- name: api
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type: STRICT_DNS
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lb_policy: LEAST_REQUEST
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health_checks:
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- timeout: 1s
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interval: 5s
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http_health_check: { path: "/health" }
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outlier_detection:
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consecutive_5xx: 5
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base_ejection_time: 30s
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load_assignment:
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cluster_name: api
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endpoints:
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- lb_endpoints:
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- endpoint: { address: { socket_address: { address: api1, port_value: 8080 }}}
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```
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### AWS ALB (Terraform)
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```hcl
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resource "aws_lb" "app" {
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name = "app-alb"
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load_balancer_type = "application"
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subnets = var.public_subnets
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}
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resource "aws_lb_target_group" "api" {
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port = 8080
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protocol = "HTTP"
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health_check { path = "/health"; interval = 15 }
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stickiness { type = "lb_cookie"; enabled = true }
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}
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```
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### Consistent hash (Python sketch)
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```python
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import bisect, hashlib
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class Ring:
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def __init__(self, nodes, vnodes=150):
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self.ring = []
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for n in nodes:
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for i in range(vnodes):
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h = int(hashlib.md5(f"{n}-{i}".encode()).hexdigest(), 16)
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bisect.insort(self.ring, (h, n))
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def get(self, key):
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h = int(hashlib.md5(key.encode()).hexdigest(), 16)
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i = bisect.bisect(self.ring, (h, ""))
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return self.ring[i % len(self.ring)][1]
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```
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### P2C (power of two choices)
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```python
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import random
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def p2c(servers, load):
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a, b = random.sample(servers, 2)
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return a if load[a] <= load[b] else b
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```
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## 매 결정 기준
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| 상황 | LB / 알고리즘 |
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|---|---|
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| AWS web app | ALB + round_robin |
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| TCP / 빠름 | NLB / HAProxy L4 |
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| gRPC, mesh | Envoy least_request |
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| Cache shard | Consistent hash |
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| DB connection pool | PgBouncer/ProxySQL |
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| Bare metal HTTP | Nginx least_conn |
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| 동질 서버 + short req | RR/Random |
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| 이질 서버 / long conn | Weighted least-conn |
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**기본값**: HTTP는 ALB or Nginx least_conn. 마이크로서비스는 Envoy.
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## 🔗 Graph
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- 부모: [[Distributed-Systems]]
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- 변형: [[Consistent-Hashing]], [[Reverse-Proxy]]
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- 응용: [[High-Availability]], [[Service Mesh]], [[CDN]]
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- Adjacent: [[API-Gateway]]
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## 🤖 LLM 활용
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**언제**: config 작성, 알고리즘 선택, troubleshoot 가설.
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**언제 X**: production tuning은 metric 기반 검증 필수.
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## ❌ 안티패턴
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- IP hash + NAT/CGNAT (모든 client가 한 노드)
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- Sticky session 과의존 → 노드 죽으면 세션 다 잃음
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- Health check 너무 짧은 interval → flapping
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- L7 LB에서 keepalive 비활성화 → 성능↓
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- Hash ring vnode 부족 → 불균형
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- TLS termination만 보고 backend mTLS 무시
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## 🧪 검증 / 중복
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- Verified (Nginx/Envoy/HAProxy docs, Mitzenmacher P2C, AWS ELB docs). 신뢰도 A.
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- 중복: 없음.
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## 🕓 Changelog
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| 날짜 | 변경 |
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|---|---|
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| 2026-05-08 | Phase 1 |
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| 2026-05-10 | Manual cleanup — Envoy/AWS/consistent-hash 코드 추가 |
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